The present invention relates to an oil application device as a component of a fixing device of an electrostatic process copying machine, an electrophotographic printer or the like.
In a fixing device of an electronic copying machine, an electronic printing machine or the like, during fixation of toner than has been transferred to a recording paper, the toner may adhere to a thermal fixing roller. To prevent the toner from soiling another recording paper, a very small amount of releasing oil such as silicone oil is applied to the thermal fixing roller using an oil application roller. Thus, toner is prevented from adhering to the thermal fixing roller, and recording papers are prevented from being stuck to one another and rolled up.
Various oil application rollers having such a function have already been proposed. For example, a cylindrical formed body made from a perforated metal hollow pipe and heat-resistant fiber is used as an oil retaining member for storing releasing oil to be applied, and an oil application amount control layer e.g. made from a polytetrafluoroethylene (PTFE) porous film is wound around the surface of the cylindrical formed body. Ends and wrapping portions of the oil application amount control layer are coated with RTV silicon rubber and bonded, so that an oil application roller is manufactured. Further, there is another oil application roller, which is manufactured by processing the oil application amount control layer as described above into a tube, covering a cylindrical oil retaining member with the tube, and heating and contracting them (see Japanese Patent Application Laid-Open No. HEI 9-185282).
Further, there is an application mechanism for copying machines, which is provided with an oil application amount control layer that has been formed through cross linkage after impregnation of voids of porous polytetrafluorethylene of the surface of a thick porous material as an oil retaining member with the mixture of silicon rubber and releasing oil (Japanese Published Patent No. HEI6-73051). That is, this application mechanism for copying machines is obtained by winding an oil application amount control layer around the surface of the thick porous material like a rolled layer, heating them at a high temperature for many hours to cause cross linkage, and thermally fusing them. This application mechanism for copying machines can suitably control releasing oil, i.e., silicone oil, and especially can stably control it over a long time even in an area where a very small amount of silicone oil is applied for oilless toner. Further, Japanese Patent Application Laid-Open No. 2000-79365 discloses an oil application device in which a felt layer is disposed on a surface of a cylindrical oil retaining member made from porous ceramics material and in which a PTFE porous film is disposed on the felt layer. This oil application device applies oil that has exuded to the felt from the oil retaining member, while controlling the oil by means of the porous film. Further, the oil application device may not necessarily be of a roller type. For example, there is known an oil application device in which oil is applied to a fixing roller by a generally flat pad.
However, in the above-mentioned oil application roller in which the oil application amount control layer is bonded with the cylindrical formed body, almost no releasing oil flows out of the bonded portion so that oil is applied unevenly, or the bonding strength is insufficient due to a small bonded area so that the oil application amount control layer is displaced or peels off. That is, it is difficult to always stably apply releasing oil to the thermal fixing roller. Further, in the oil application roller manufactured by heating and contracting the tubular oil application amount control layer, the oil application amount control layer tends to be heated and contracted inhomogeneously, and the pore diameter is inconsistent. That is, it is difficult to always stably apply releasing oil to the thermal fixing roller. Furthermore, in the application mechanism for copying machines, when the oil application amount control layer is thermally fused with the thick porous material, heating must be carried out for a long time at a high temperature. Thus, the process tends to be too troublesome. Further, in the application device that applies oil that has exuded to the felt from the oil retaining member while controlling the oil by means of the porous film or in the application device that applies oil to the fixing roller by means of a pad-like structure, the same problem as described above arises as to a method of bonding the oil application amount control layer to the top surface layer. Namely, also in this case, no releasing oil flows out of the bonded portion so that unevenness of application is caused, or the bonding strength is insufficient due to a small bonded area so that the oil application amount control layer is displaced or peels off. This leads to a problem of fluctuations of application amount of oil. Furthermore, in a so-called inoperative state other than application, e.g., in a state from shipment to preservation of products, it is also required that oil in the oil retaining member be prevented from exuding from the oil application amount control layer. Such exudation of oil causes a problem of excessive application of oil at the beginning of an application process when restarting the application device.
It is thus an object of the present invention to provide an oil application device in which releasing oil can be uniformly applied to a thermal fixing roller, in which an oil application amount control layer is not displaced or does not peel off during operation, and which can be bonded with an oil retaining member easily. It is another object of the present invention to provide an oil application device in which no oil exudes from an oil application amount control layer e.g. in a still-standing state from shipment to preservation of products.
Under such circumstances, the inventors discovered the following facts as a result of careful and detailed research and succeeded in completing the invention. That is, if an oil application amount control layer is bonded with an oil retaining member for retaining application-use silicone oil by means of the mixture of adhesive and mixture-use silicone oil, the mixture is in a state of dispersal of the adhesive and the mixture-use silicone oil. Thus, the oil application amount control layer is bonded with the oil retaining member due to the hardening of the adhesive. In the oil application amount control layer, closed-pore portions and unclosed-pore portions with interposition of the unhardened mixture-use silicone oil are dispersed through each other. This bonded portion in a state of dispersal prevents the oil application amount control layer from being displaced or peeling off, and the mixture-use silicone oil in its dispersed state serves as an oil passage and makes it possible to uniformly apply application-use silicone oil to a thermal fixing roller. If the ratio of the viscosity of application-use silicone oil to the viscosity of mixture-use silicone oil is in a certain range, i.e., if the viscosity of application-use silicone oil is relatively close to the viscosity of mixture-use silicone oil, no oil exudes from the oil application amount control layer in a still-standing state.
That is, the first invention of the present invention provides an oil application device wherein an oil application amount control layer is bonded with an oil retaining member for retaining application-use silicone oil, using the mixture of adhesive and mixture-use silicone oil, and wherein the ratio (VKS)/(VTS) of a viscosity (VKS) of the mixture-use silicone oil at 25xc2x0 C. to a viscosity (VTS) of the application-use silicone oil at 25xc2x0 C. ranges from 50/1 to 1/10. According to this construction, the oil retaining member and the oil application amount control layer are bonded together while being dispersed as a whole due to the hardening of the dispersed adhesive, and the oil application amount control layer guarantees a passage for the application-use silicone oil while being dispersed as a whole due to the dispersed mixture-use silicone oil. Further, since diffusion (infiltration) of the application-use silicone oil into the mixture-use silicone oil existing as an oil passage is suppressed in a still-standing state, no silicone oil exudes to the surface of the oil application amount control layer.
Further, the second invention of the present invention provides an oil application device wherein an oil application amount control layer is bonded with an oil transfer layer that is provided on an oil-application side of an oil retaining member for retaining application-use silicone oil, using the mixture of adhesive and mixture-use silicone oil, and wherein the ratio (VKS)/(VTS) of a viscosity (VKS) of the mixture-use silicone oil at 25xc2x0 C. to a viscosity (VTS) of the application-use silicone oil at 25xc2x0 C. ranges from 50/1 to 1/10. According to this construction, even in the case where the oil transfer layer for preventing uneven application is provided between the oil retaining member and the oil application amount control layer, the same effect as described above can substantially be achieved.
Further, the third invention of the present invention provides an oil application device wherein the viscosity (VKS) of the mixture-use silicone oil at 25xc2x0 C. is equal to the viscosity (VTS) of the application-use silicone oil at 25xc2x0 C. According to this construction, diffusion (infiltration) of the application-use silicone oil into the mixture-use silicone oil is further suppressed, not to mention that the same effect as described above can substantially be achieved during nonuse. Therefore, it is possible to reliably prevent silicone oil from exuding to the surface of the oil application amount control layer.